Vacuum on 1968 GTS 340 4 spd.

The lifters' pistons 'typically' have a gauranteed range of up to .120-160".... But some have more. Running the .050" to .080" range gets you roughly in the middle of the 'typical' range. Also note that is can vary between each rocker/pushrod/valve, so if you can do a couple of valve this way, it would not hurt. A valve sunk into the head from a valve job can stick up further than its neighbors and push the pushrod in even further; deck heights can vary; rocker and rocker/shaft wear can vary.

And, the pushrods typically only bend if things get so out of whack that a valve hits a piston.

If you have an old spare pushrod or just buy a cheap new one, you can make your own checker by cutting out a 1" section up near one end, threading the inside, and putting a piece of skinny all thread between the end with locknuts. That is they are!